Jerry Brown is the governor of California. He spoke ahead of the UN Secretary-General's Climate Leadership Summit about politics and the value of his state's emissions trading system in building a healthier, cleaner future. The state's economy is growing, and its climate work is setting a pace for the nation.

"The science of climate change, of course, is very clear. The politics – not so.

The politics of climate change are murky, uncertain, and often totally ineffective. That’s why it’s good to take a look at what’s happening in California. This state has a program to deal with carbon pollution, to encourage renewable energy, electric cars, efficient buildings and appliances.

And despite taking the leading role in combating climate change in the United States, if not in the world, our economy is not only recovering, it is expanding at a greater rate than the rest of the country. Not that we don’t face our barriers and obstacles and even political opposition, but we are carrying on because we know in California that carbon pollution kills, it undermines our environment, and, long-term, it’s an economic loser.

There has to be a price on carbon, because there is a price on carbon - it’s the consequences to health, to the economy, and to our climate. We face an existential challenge with the changes in our climate. The time to act is now. The place to look is California. We’re not finished, but we sure are setting the pace."